..those who live in glass houses should not throw stones...

I am having a discussion with my son about what this means exactly. We have two different opinions on why stones should not be thrown by these people. One of these focuses on being attacked, and the other one focuses on self-destruction.

First one- The person throwing the stones is outside of the house.

Therefore, because you have a weak foundation you are vulnerable to attack..or other stones being thrown back at you...and breaking your house.

or

Second one- The person throwing the stones is inside of the house.

Therefore, because if you are vulnerable, anything physically able to destroy your surroundings should not be used offensively, as you can damage yourself.

We cannot find anything on the internet that specifically defines what this term is supposed to mean, and where the rock-throwing is actually standing. Does anyone have an educated opinion?

I always took it as that as a person living in a glass house, you shouldn't throw stones at others as you are in the same predicament that they are and, therefore, can crumble just as easily.